The present invention is concerned with a hydrodynamic brake of the kind comprising a rotor bucket wheel and a stator bucket wheel which together form a torus-shaped working chamber which can be filled with working fluid, and between which there is located a bucket wheel gap which is arranged at least approximately perpendicular to the axis of the rotor bucket wheel. Such a brake also includes a casing which is attached to the stator bucket wheel and which encompasses the rotor bucket wheel. The casing has an annular outlet duct extending around the rotor bucket wheel.
Baffle-type flow obstructions are arranged in an accommodating space extending along the outer circumference of the bucket wheels and are able to move around the circumference of the bucket wheel gap in such a way that they can be disengaged when the brake is disengaged. In addition to the bucket wheel gap, an additional gap is provided between the greatest external diameter of the rotor bucket wheel and the casing, and this defines the annular outlet duct.
A similar brake is known from German Laid-open Patent Specification No. 19 42 475. However, in this known brake, there is no gap adjacent to and surrounding the perimeter of the bucket wheel gap to define the annular outlet duct, which duct is also the accommodating space for the baffle-type flow obstructions.
In the brake of the kind to which the invention pertains, that part of the casing which defines the outermost circumference of the annular outlet duct has a relatively small clear diameter. This means that this part of the casing, together with the outer circumference of the rotor bucket wheel, forms a narrow gap immediately adjacent to and surrounding the perimeter of the bucket wheel gap. In this way a reduction in the weight of the casing is reduced. At the same time, the filling volume of the brake is reduced and with it the filling time. As a result, a quicker braking response is obtained. The bucket wheel gap is substantially sealed off from the annular outlet duct, facilitating the achievement of an orderly flow. The accommodating space for the plate-type baffles in this embodiment is also reduced to a gap-type annular space which is generally located between a flange secured to the stator bucket wheel and a flange secured to the casing. The engagement and disengagement of the baffles are generally effected with the aid of a pressure medium adjustment cylinder.
In a brake of this kind, it has been observed, among other things that the baffles accidentally become engaged in the working chamber, against the force exerted by the adjustment cylinder, when the brakes are engaged. This reduces the braking effect to an unacceptable extent.
It is believed that the accidental engagement of the baffles is caused by the occasional extremely high flow speed attained by the working fluid in passing through the radially outermost region of the working chamber from the bucket ducts of the rotor into the bucket ducts of the stator. It is certain that the high flow speed greatly reduces the static pressure set up in the bucket wheel gap, and in the extreme case, reduces the pressure to virtually zero. Furthermore, it is assumed that a small part of the flow of working fluid penetrates into the space provided to accommodate the baffles, and that in the radially outermost region of this accommodating space, the flow energy is converted to static pressure, so that higher static pressure is created there. The difference between the static pressures which prevail respectively in the radially outermost region and in the radially innermost region of the baffle space can thus from time to time force the baffles into the bucket wheel gap against the force produced by the adjustment cylinder to maintain the baffles in their disengaged state.
At first it was attempted to solve the problem by withdrawing the baffles further outward when the brake was engaged. However, this would necessitate enlarging the displacement path, and possibly also increasing the external dimensions of the brake. For this reason, pressure venting of the radially outermost region of the baffle-accommodating space was considered. This solution meant providing a connection line from the baffle space to a zone at lower pressure outside the brake housing. However, if this were done, it would then be necessary to conduct the quantity of working fluid escaping via such a venting line back into the working chamber.